We visited Blue Lagoon from the Carnival Glory in December 2021 as a shore excursion, with the sea lion experience. In short we recommend it as an easy family friendly day trip from the cruise ship terminal. A tender/water taxi will take you to the island right from the cruise dock.
Blue Lagoon offers several packages, including sting ray encounter, sea lion encounter, and dolphin encounter. The facility's are all modern, ample bathrooms, and there are simple snacks for purchase and a buffet. It seems some people can buy the buffet as part of the cruise excursion...but it's $27 per person on island...OR hint...hint...go to the bar and buy a kids buffet (burger or hotdog , with fries, and drink) for $6. Or bring some snacks from your boat.
The beaches were nice, mask were worn and hand gel stations are out. One of the encounters + a meal+ getting your photos paid for will consume most of your time before your designated return time. So if you want beach time you may want to decide to cut something out.
The sea lion encounter was fun! They have several. The first sea lion we were to interact with wasn't feeling it and just ignored the trainer and took a nap on the dock lol. They explained they don't force it so she went and found another that was excited to come interact and play with us a bit. You wear life vests, walk on a floating dock and stand on a platform about 3 feet under water and interact in a structured playful way with the trainer and sea lion. After the encounter, you go to a land area where they take cute photos with the sea lion. When done there are clean bathroom facilities to clean up if you brought a change of clothes, etc. A photo lab is available and you can purchase the photos with cash or credit card (Amex NOT accepted anywhere on the island). The whole island had good free guest wifi if needed.